1. Field of the Invention
The invention is in the field of partial oxidation of hydrocarbonaceous gases.
2. Description of the Prior Art
Partial oxidation processes, both in the gaseous and in the liquid phases, have been known in the art for many years. It has long been known, for example, that methane may be partially oxidized to formaldehyde at low pressures (near atmospheric pressure), and that a substantial conversion of methane to methanol, as well as formaldehyde, occurs at elevated pressures, usually between about 50 and about 200 atmospheres. Some of the more successful experiments at elevated pressures were performed by E. H. Boomer and V. Thomas, Canadian Journal of Research, Vol. 15, Sec. b, 414-433 (1938), using 3%-7% of oxygen in methane at 475.degree. C. and 140-220 atmospheres. They investigated the effect of various parameters, including "catalytic" effects of various solids; and they concluded (p. 433) that "the conversion of total carbon in the system to methanol is very low, and probably not of commercial value even in a circulatory system."
In view, however, of the apparent simplicity of the process, and the large availability of natural gas at relatively high pressure, there have been numerous experiments and even attempts to commercialize the partial oxidation of methane, but none has heretofore been successful. Except for the gas/catalytic oxydehydrogenation of normal butylenes to butadiene, and some early gas phase partial oxidation of propane and butane, the more commercially successful partial oxidations, particularly of alkanes, have been in the liquid phase, at relatively low temperatures, as very recently summarized by J. E. Lyons, Hydrocarbon Processing, Nov. 1980, 107-119.
Even in the case of low pressure partial oxidation of methane to formaldehyde there has, to applicant's knowledge, been no commercialization, at least in Western countries. The primary reasons for this surprising lack of success have been the relatively low yields, and the complex mixture of products and contaminants produced, especially in the case of partial oxidation of higher alkanes. Low yields result from the fact that the desired partial oxidation products are much more readily further oxidixed to undesired carbon monoxide, carbon dioxide and water than is the parent hydrocarbon, and this adverse factor is especially the case with methane--much the hardest to react of all hydrocarbons. Thus, the only very high ratios of hydrocarbon to oxygen can increase the probability of the desired, as compared to the undesired, reactions occurring. And, in consequenoe, very low yields per pass occur.
Furthermore, as Boomer and Thomas report, the presence of ordinary materials of commercial construction, especially steel and its alloys, has an erratic and adverse effect upon yields. While copper and silver materials of construction provided good means for heating the charge, they tended to promote further oxidation of the desired methanol to undesired formaldehyde and formic acid. Furthermore, since water vapor is also a substantial product of the reaction, it is necessary to separate the products from water, which is notoriously difficult in the case of formaldehyde and formic acid, and particularly so in the presence of methanol--which forms hemiacetals and acetals with formaldehyde and methyl formate with formic acid, both sets of reactions being catalyzed by formic acid itself.
Still other problems involve preheating, maintaining and controlling the reaction temperature, and usefully recovering the substantial heat produced by the partial oxidation reaction, particularly since very large amounts of gases must be heated and reacted in comparison to the amount of product produced.